In recent years there has been a significant increase in the popularity and the use of electronic video games. Typically video games are displayed and played on the screen of a conventional television receiver. The variety and the complexity of electronic video games have increased by the use of a digital microprocessor in a game player console. In one form, these games include the microprocessor packaged with a preprogrammed read only memory (ROM) and player actuated spot position control potentiometers, which permit the spot position of a character, the characters being representative of game players, to move around on the television screen. Each preprogrammed memory contains a set of program instructions for a particular video game. By replacing one preprogrammed memory with another preprogrammed memory, a completely new game may be played.
The interconnection of two or more video games may then become desirable. One such arrangement is hinted at in the publication by T. A. Waldow, "The Xerox Alto Computer," Byte Magazine (September 1981), pp. 58-68. To interconnect the games the Wadlow arrangement uses a Carrier Sense Multiple Access System with Collision Detection (CSMA/CD) such as disclosed in U.S. Pat. No. 4,063,220, issued Dec. 13, 1977. On the one hand, a CSMA/CD System communicates packets of information and operates at bit rates in the order of 3 megabits per second. On the other hand, a standard telephone line operates at bit rates in the order of 300 bits per second. This raises a dilemma. How can high speed video games be competitively played between users who are interconnected over low speed standard telephone lines?"
Unfortunately, the communications between video games connected over telephone lines can be constrained in any of several ways. For example, each movement of a player actuated spot position control potentiometer, which may be embodied in the form of a joystick or a keyboard, typically provides in parallel a few bits of position data. The position data can be "squeezed" through a console port and converted, if need be, to a serial form for transmission between the games. Since the telephone line which is here assumed to be the data transmission link, is low speed, the absolute amount of information that can be exchanged between real time action games is limited. Otherwise, a significant delay in communications between games would likely occur.
Another constraint is found in synchronizing geographically separated games. In order for both video games to stay synchronized, one should communicate to the other what the one is actually doing. However, as priorly mentioned, (a) the telephone line is a low speed serial transmission link and (b) a limited amount of data is exchanged. The problem then is to determine an arrangement for exchanging a relatively small amount of data so that the games are likely to be, and to remain, synchronized.
Still another constraint can be found in detecting and correcting transmission errors. Noise across the telephone line can ordinarily impede the data communication link. Since burst errors are possible, an appropriate arrangement is also desired to detect and correct transmission errors.